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Armstrong will star as St. Jimmy in eight performances of the production from September 28 through October 3. The play is a rock opera that follows the story of a musician named Johnny who is haunted by St. Jimmy, an apparition that helps fuel Johnny's drug addiction.

Tony Vincent usually plays the role of St. Jimmy, but he is leaving the production until October 12 to attend to a family matter. Understudies will fill the role the second week as Armstrong will join his fellow band mates in Caracas, Venezuela, to start a South American tour.

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Armstrong will be making his Broadway debut as a performer with his turn in "Idiot." However, he's helped promote the musical and he's also a co-writer of the book based on the production.

"American Idiot" won two Tony Awards, best sets and best lighting for a musical, but lost best musical to "Memphis.